It's funny... the things that drive you over the edge and force you to post in ATS again....
Originally posted by CogitoErgoSum1
The Hayflick limit is the limit of the maximum number of cell replications that a human being (or any species). When you can't replace your cells
anymore, you die. And Leonard Hayflick calculated that number for a variety of species, and for human beings it was 120.
CES1, I believe that Nygdan understands what you are saying very well. His point is that the Hayflick Limit was determined for cells in
that is suspended in medium. This is a distinct situation. Technically what the Hayflick limit describes is the number of times cultured cells will
divide without being immortalized. The simple fact of the matter of is that human cells can divide more than 50 times. I’ve got a couple of lines of
human kidney cells that have divided hundreds of times. HELA cells, a cell that can be purchased from any vendor, were harvested from a woman named
HEnrieatta LAck, and have been grown in culture longer… well probably longer most ATSer’s have been alive. I think embryo to adult is something
like 23 cell divisions alone. Your skin cells divide one whole heck of a lot more than 50 times. What about sperm? Sperm cells are produced daily…
how do you think they arise?
Admittedly HELA and other immortalized cell lines are not in a ‘natural’ genetic state, but then again neither were Hayflick’s cells in culture.
The point is this: The number of times a cell will divide in culture implies nothing about how many times it will divide in an organism.
I don’t see how this doesn’t make sense. It’s the reason why hamsters generally live for a couple years or why dogs only live for a
certain length of time all species have a limit on how many times their cells can replicate themselves before they start to die off.
When an organism dies is related to the number of times a cell can divide, but this is not likely dictated via some type of chronological bookkeeping.
One of the primary things that controls this is the state of the cells genetic information, including, but not limited to: Telomere length, unrepaired
‘nicks’ in DNA, repression/activity of certain genes, oxidative damage, and overall cellular health as a function of ‘feast’ and ‘famine’
conditions. Cells grown in culture are more likely to see all types of genetic damage.
I understand this test was conducted in a cultured environment so you are free from diseases, mutations or anything else that would hamper cell
LOL… Culture environments free from disease!!! Apparently you’ve never grown Mammalian cells before! Mammalian cells are tough to grow, they get
infected by everything, E. Coli, mycoplasmas, etc. I’ve been in labs that have literally had to stop work for months because they couldn’t resolve
Contamination issues aside, no environment is free from mutation, especially the cultured environment. I don’t want to get into a big discussion
about mutation here (saving it for the ‘Origins’ threads when I can commit to getting back over there), but a culture environment is not ‘free
Bottom line is your cells can only replicate themselves so many times. This has been proven, however I am not including gene manipulation or
anything of that nature to extend human life.
Bottom line is that post-differentiation many mammalian cells are programmed to divide rarely or not at all. Other cells however continue to divide as
a necessary function of their existence (think
). What Hayflick found is not directly applicable to cells in vivo
How does this mesh with the findings that have increased lifespan of C. Elegans? Is C. Elegans somehow immune to the concept of Hayflick’s Limit?
Anyway… and again not to change the topic of this thread, I thought Noah lived to be like 900 or something….
[edit on 4-11-2005 by mattison0922]